The present invention relates to a support for resin-coated-paper type photosensitive materials which is obtained by coating a paper substrate (hereinafter referred to as "base paper") composed mainly of natural pulp with a resin having film-forming properties, preferably a polyolefin resin. Particularly, it relates to a support for resin-coated-paper type photosensitive materials which exhibits good photographic properties when a silver halide photosensitive emulsion layer is provided thereon.
Supports for resin-coated-paper type photosensitive material which are obtained by coating at least one side of a substrate with a resin having film-forming properties, are well known. For example, Jap. Pat. Pub. No. SHO 55 (1980)-12584 discloses a technique concerning a support for photosensitive materials which is obtained by coating base paper with a resin having film-forming properties, preferably a polyolefin resin. U.S. Pat. No. 3,501,298 discloses a technique concerning a support for photosensitive materials which is obtained by coating both sides of base paper with a polyolefin resin. Since the employment of a quick processing method for development of silver halide photographic photosensitive materials, supports for photosensitive material which are obtained by coating both sides of base paper with a polyethylene type resin have been mainly used in practice for producing photographic paper. Depending on requirements, a titanium dioxide pigment is usually included in a resin layer on one side, i.e., the image-forming side in order to impart a fine definition.
However, supports for resin-coated-paper type photosensitive materials which are obtained by coating base paper composed mainly of natural pulp with a resin having film-forming properties have had an inherent and serious problem affecting harmfully on photographic properties of a silver halide photosensitive layer when it is applied thereon.
To describe the problem in detail, when a silver halide photosensitive material produced using as support, a resin-coated paper obtained by coating base paper composed mainly of natural pulp with a resin having film-forming properties is stored after production, in particular, when the photosensitive material is stored under a high temperature and a high humidity circumstance, the silver halide of the photosensitive material undergoes spotty fog with an increase of the storage period, so that the unexposed portion has developable spots during development processing, or that sensitivity of the photosensitive material is decreased or increased spot-wise. For example, in the case of a certain positive type black-and-white silver halide photographic paper, spotty fogs occur on a white background. The spot-wise fog has a diameter of as large as twenty and several millimeters in some cases, and the photographic paper loses its commercial value completely. In the case of a photosensitive material of a certain type using a silver complex diffusion transfer process which comprises the resin-coated paper as a support for a silver halide negative photosensitive layer, fogs develops spot-wise in the [negative] silver halide photosensitive layer, image to be transferred therefrom and formed on a positive sheet is low in density spot-wise, or is hardly formed. Therefore, that photosensitive material loses its commercial value completely. In the case of multi-layered silver halide color photographic paper of a certain type comprising the resin-coated paper as support and color developing layers provided thereon in the order of yellow, magenta and cyan, fogs develops spot-wise in those layers, particularly, in yellow and magenta color layers, where sensitivity deteriorates spot-wise, so that color balance of image to be developed is upset and that photosensitive material loses commercial value. Hereinafter, the defective phenomena described above are generically called "the spot trouble".
There have been proposed various stabilizers or fog inhibitors for preventing the change of the photographic characteristics of silver halide photosensitive materials during storage. However, the addition of the various stabilizers or fog inhibitors in a layer constituting a silver halide photosensitive material comprising resin-coated paper as support has been hardly able to eliminate the spot trouble; moreover, use of them has tended to bring about no small and harmful effects on the photographic performance such as sensitivity degradation, contrast degradation, etc.
There are several proposals concerning the photographic properties of supports for photosensitive materials. In Jap. Pat. Pub. No. SHO 54 (1979)-9884, there has been proposed a non-fogging support for resin-coated paper type photosensitive materials which is obtained by coating base paper with a polyolefin resin containing a hydroxy-substituted triazolopyrimidine compound. An embodiment of this art, however, proved to be too poor to eliminate the spot trouble of a silver halide photosensitive material making use of the support. As to paper for photography, it has been proposed in Jap. Pat Appln. Kokai (Laid-Open) No. SHO 52 (1977)-65423 and Jap. Pat. Pub. No. SHO 58 (1983)-43730 to remove the undesirable influence of the decomposition of a cationic electrolyte and additives for paper, respectively, on photographic properties. In silver halide photosensitive materials obtained by using as support, resin-coated paper comprising such paper for photography, the spot trouble cannot be prevented at all, and it has been proved that the spot trouble is caused by a mechanism utterly different from the mechanisms described in the specifications of the above references. In Jap. Pat. Appln. Kokai (Laid-Open) Nos. HEI 2 (1990)-96741, HEI 2 (1990)-99689 and HEI 2 (1990)-99693, there have been proposed techniques for improving the photographic properties of unbleached kraft paper. These techniques can impart satisfactory photographic properties to bleached kraft paper but unsatisfactory photographic properties to unbleached kraft paper. The cause for this is that propylene oxide and/or silicone compound used in a defoaming agent used before bleaching step remain in base paper. It has been proposed to improve the photographic properties of unbleached kraft pulp by specifying a defoaming agent and a cold water extraction pH of the pulp. However, in a silver halide photosensitive material obtained by using as substrate, resin-coated paper comprising base paper composed mainly of bleached natural pulp prepared by applying the aforesaid technique, the spot trouble cannot be prevented at all, and it has been proved that the spot trouble is caused by a mechanism utterly different from the mechanisms described in the specifications of the above references. In addition, in Jap. Pat. Pub. No. SHO 58 (1983)-43732, there has been proposed a technique for improving the shelf life of a silver halide photographic material by using resin-coated paper comprising base paper composed mainly of natural pulp bleached by the use of a peroxide at a alkaline pH. But, the employment of this resin-coated paper permits insufficient prevention of the spot trouble. Furthermore, in Jap. Pat. Pub. No. SHO 59 (1984)-38575, there has been proposed a technique for preventing the fog and the spot trouble of a silver halide photographic material by the use of paper for photography made of wood pulp obtained by the oxygen pulping process. But, the employment of resin-coated paper comprising the paper for photography as substrate also permits insufficient prevention of the spot trouble.
As described above, there have not been known at all a technique for removing the spot trouble of a silver halide photosensitive material comprising as substrate, resin-coated paper obtained by coating base paper composed mainly of natural pulp with a resin having film-forming properties, and a mechanism or cause of the occurrence of the spot trouble. Moreover, the spot trouble has not been able to be removed at all by a conventional technique.